2010 07 captcapt.pku.edu.cn/docs/20180606134549941531.pdf · intensity at focus ~ 7 1019 w/cm 2 rcf...
TRANSCRIPT
Andreas Henig
J. Schreiber, D. Kiefer, D. Jung, R. Hörlein, P. Hilz, K. Allinger, J. Bin, S. G. Rykovanov, H.-C. Wu, X. Q. Yan, V. Liechtenstein,
J. Meyer-ter-Vehn, T. Tajima, F. Krausz, D. Habs
K. Flippo, C. Gautier, L. Yin, B. J. Albright, S. Letzring, R. Johnson, T. Shimada, J. Fernandez, B. M. Hegelich
S. Steinke, T. Sokollik, M. Schnürer, P. V. Nickles, W. Sandner
M. Geissler, K. Markey, M. Zepf
opaque target
hot electrons generate quasi-static E-field (TV/m)
ions are accelerated from the back surface (MeV/u)
large transverse spreading of E-field (100s of m)
energy transfer to electrons spatially separated from ion acc.
stationary instead of co-propagating acceleration field
exponential spectrum (low conversion efficiency to highest energetic ions)
But:
ASE pedestal / prepulses preceding the main peak
target thickness limited by heating / shock breakout
optimum target thickness decreases with ASE duration
M. Kaluza et al., Phys. Rev. Lett. 93, 045003 (2004) What would be the optimum for
a nearly background-free pulse?
for high intensities / ultra-thin targets, the laser will either directly (thickness d < skin depth ls) or eventually
(depletion of electron density / relativistic transparency) penetrate the foil
volumetric energy transfer to foil electrons ↔ reduced total absorption
empirical law for optimum areal density opt:
opt / ncr 3 + 0.4 (I/I1)1/2
I1 = 1.368 1018 W/cm2 ( m/ )2
at I = 7 1019 W/cm2, ne/ncr = 660, = 1053 nm:⇒ dopt 10 nmEsirkepov et al, Phys. Rev. Lett. 96, 105001 (2006)
Proton maximum energies from Al/H+ double-layer targetvs. areal density and intensity I (from 2D PIC simulations)
thickness 2 nm - 60 nm
bulk density (2.7±0.3) g/cm3 (75 % sp3)
damage threshold: 1011 W/cm2 @ 500 fs, 108 W/cm2 @ 1.2 ns
high percentage of sp3 bonds gives diamond-like properties
high radiation and heat resistence
high tensile strength
50 nm DLC foil - proton beam profile
14 MeV43°
20 MeV30°
25 MeV18°
1053 nm700 fs FWHM80 Jps-contrast ~ 10-8
/4 waveplate for polarisation adjustmentKDP crystal,3 mm thickness, 200 mm
intensity at focus~ 7 1019 W/cm2
RCF stackproton beam profile
Thomsonparabolaspectrometer
double plasma mirrorreflectivitytot ~ 50 - 60%40 - 50 J energy throughputresulting ps-contrast ~ 10-12
ultrathin foil targetsdiamond-like carbon (DLC) foils50% sp3, high mechanical stability, radiation hardness10 - 50 nm thickness
1 mm
CR39 / image plates
simple analytical model derived to predict the instantaneous laser intensity at burn-through time (i.e. I (t1))
relativistic transparency / BOA regime:highest ion energies generated for max. I (t1)
Etarget = 90 J540 fs FWHMIpeak 2 1020 W/cm2
new OPA-based frontend resulting in high contrast on target without plasma mirrors, increased peak intensity of Ipeak 2 1020 W/cm2
optimum thickness increases as expected, highest ion energies at 58 nm:
C6+ max. energy:0.5 GeV
advanced analytical model to predict ion energies:
data spanning over wide range of target thicknesses
beginning: target opaque, TNSA-like acceleration
t1: ne / (ncr ) ~ 1, target becomes relativistically transparent
short period of strong ion acceleration until t2: ne / ncr ~ 1
highest ion energies observed at 8.5° angle orthogonal to laser polarization
0 10 20 30 40 50 600
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Ion
Cut
-Off
Ene
rgy
[MeV
/am
u]
target thickness [nm]
exp. H+ (a0=3.6)
sim. H+ (a0=3.6)
exp. C6+ (a0=3.6)
sim. C6+ (a0=3.6)
exp. H+ (a0=5.0)
exp. C6+ (a0=5.0)
- - - H+
theo. TNSA
(cp. Andreev et al.)
10 Hz Ti:sapph system, 45 fs FWHM, 0.7 J on target after DPM (contrast ~ 10-12)peak intensity up to 5.3 1019 W/cm2 (a0 = 5), linear polarization
5 nm DLC (a0 = 5):
13 MeV protons71 MeV C6+ ions
4
5
6
7
Carbon C6+
protons
104
105
106
107
10 20 30 40 50 60 70 80 900energy (MeV)
part
icle
num
ber
(MeV
-1 m
sr-1)
Carbon C6+
protons
optimum thickness just below skin depth: dopt < ls = c / p
J. Fuchs et al., Nature Physics (2006)
TNSA- scaling according to fluid-model predictions:
J. Fuchs et al., Nature Physics (2006)
TNSA- scaling according to fluid-model predictions:
much increased maximum energy and conversion efficiency:
0 10 20 30 40 50 400 600 800 10000
1
2
3
4
5
6
7
8
9
10
11
12
13
co
nv
ers
ion
eff
icie
ncy
(%
)
target thickness (nm)
H+ (E > 2MeV)
C6+
(E > 5MeV)
sim C6+
sim H+
0,0 0,2 0,4 0,6 0,8 1,00,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
0,45
0,50
an
gle
[d
eg
]
an
gle
[ra
d]
PIC
FIT -0.34 x + 0.34
normalized energy
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
RCF
0 2 4 6 8 10 121
10
100
1000p p ( p)
pro
ton
@1
14
nsr
(E
= 3
%)
DPM & DLC 5nm (CE = 1.6%)
no DPM 1μm Titan (CE = 0.13%)
1.6% into protons10.5% into C6+ ions
5 nm DLC (a0 = 5): 1 m Ti (a0 = 7):
0.13 % into protons
First experiment showing the correlation of relativistic transparency enabled laser penetration and enhanced ion energies using nm-scale DLC foils and a DPM-setup at TRIDENT
World record 0.5 GeV carbon ions generated at upgraded TRIDENT, sufficient for fast ignition in ICF
13 MeV protons and 71 MeV C6+ from a small-scale, high rep. rate Ti:sapph laser system with pulse energies as low as 0.7 J
But: so far only monotonically decaying ion energy distributions
Many potential applications (such as IBT or FI-ICF) require quasi-monoenergetic spectrum
Route towards intrinsically monochromatic ion beam generation needed
whole target gets accelerated, light sail driven by radiation pressure = intensity / c
whole target gets accelerated, light sail driven by radiation pressure = intensity / c
Photo courtesy The Planetary Society
small intensities (0.14 W/cm )“infinite” acceleration times (years)
JFL Simmons et al, Am J Phys 1993 (Marx Nat 1966 )
whole target gets accelerated, light sail driven by radiation pressure = intensity / c
Photo courtesy The Planetary Society
small intensities (0.14 W/cm )“infinite” acceleration times (years)
JFL Simmons et al, Am J Phys 1993 (Marx Nat 1966 )
high power (1015 W)high intensities (>1021 W/cm )short acceleration times (10’s, 100’s fs)ultrathin foils required5 nm, 2 m focus: 5J rest energy
Klimo et al, Phys. Rev. ST Accel. Beams 11, 031301 (2008)
electron spectrum
1D PIC simulation, 32nm foil thickness, 100fs pulse duration (sin ), 1.5 1020 W/cm
electron spectrum ion density ion density
1D PIC simulation, 150nm foil thickness, 64fs pulse duration (sin ), 2 1021 W/cm
Robinson, Zepf et al., New J. Phys. 10, 013021 (2008)
proton spectrum proton spectrum
linear polarization circular polarization
1D PIC simulations (by Sergey Rykovanov)
linear polarization circular polarization
strong electron heating
foil explosion
electrons remain cold
ballistic neutral foil acceleration
formation of compressed, highly dense electron layer
characteristic loops in ion phase space
key to success: suppression of electron heating
opt / ncr = (I/I1)1/2optimum condition:
a) b)
z z
ni
ni
ne
ne
EzEz
c)
0 0 z0ld ld + lc
ne0
Ez0
nec
electrondepletion
layer
compressedelectron
layer
pz
ld + lc
ionphasespace
evolution
t1
t2
t3
0 5 10 15 2520 30 35 40 50target thickness (nm)
45
15
10
5
0
max
. ion
ene
rgy
(MeV
/ u) H+
C6+
lin.
lin. circ.
circ.
elec
tron
num
ber
(a. u
.)
energy (MeV)
lin. circ.
0.5 1.0 2.01.5 2.5 3.0
1010
109
electronspectrum
d = 5.3 nm
maximum ion energy vs. target thickness
electron spectrum at optimum thickness
optimum thickness d = 5.3 nm consistent with condition opt / ncr = (I/I1)1/2
circular polarization results in significant reduction of electron heating
0 10 20 30 5040 60 70 80 90energy (MeV)
part
icle
s (M
eV-1 m
sr-1) 107
106
105
carbon C6+
protonscarbon C6+
protons
linearpolarization
circularpolarization
0 10 20 30 5040 60 70 80 90energy (MeV)
part
icle
s (M
eV-1 m
sr-1) 107
106
105
circularpolarization
0 10 20 30 5040 60 70 80 90energy (MeV)
1
10
100
part
icle
s (a
. u.)
t = 45 fst = 221 fs
linearpolarization
0 10 20 30 5040 60 70 80 90energy (MeV)
1
10
100
part
icle
s (a
. u.)
carbon C6+t = 45 fst = 221 fscarbon C6+
experiment
simulationsimulation
experiment
0
0.02
0.04
0.06
0.08
circularpolarization
3.0 3.1 3.2 3.3 3.4 3.5x (λ)
p x (m
i c )
carbon C6+
t = 45 fs
0
0.02
0.04
0.06
0.08
3.0 3.2 3.4 3.6 3.8 4.0x (λ)
p x (m
i c )
linearpolarization
carbon C6+
t = 45 fs
measured proton and C6+ spectra
0 10 20 30 5040 60 70 80 90energy (MeV)
part
icle
s (M
eV-1 m
sr-1) 107
106
105
carbon C6+
protonscarbon C6+
protons
linearpolarization
circularpolarization
0 10 20 30 5040 60 70 80 90energy (MeV)
part
icle
s (M
eV-1 m
sr-1) 107
106
105
circularpolarization
0 10 20 30 5040 60 70 80 90energy (MeV)
1
10
100
part
icle
s (a
. u.)
t = 45 fst = 221 fs
linearpolarization
0 10 20 30 5040 60 70 80 90energy (MeV)
1
10
100
part
icle
s (a
. u.)
carbon C6+t = 45 fst = 221 fscarbon C6+
experiment
simulationsimulation
experiment
0
0.02
0.04
0.06
0.08
circularpolarization
3.0 3.1 3.2 3.3 3.4 3.5x (λ)
p x (m
i c )
carbon C6+
t = 45 fs
0
0.02
0.04
0.06
0.08
3.0 3.2 3.4 3.6 3.8 4.0x (λ)
p x (m
i c )
linearpolarization
carbon C6+
t = 45 fs
measured proton and C6+ spectra
Hegelich et al. (TNSA): 20 J laser pulse energy
0 10 20 30 40 50 60 70 80 90
105
106
107
energy (MeV)
part
icle
s (M
eV1 m
sr1 )
Hegelich et al., Nature 2006 Henig et al., PRL 2009
Henig et al. (RPA): 0.7 J laser pulse energy
40 times increased conversion efficiency
comparison with TNSA, Hegelich et al., Nature 439, 441 (2006):
0 10 20 30 5040 60 70 80 90energy (MeV)
part
icle
s (M
eV-1 m
sr-1) 107
106
105
carbon C6+
protonscarbon C6+
protons
linearpolarization
circularpolarization
0 10 20 30 5040 60 70 80 90energy (MeV)
part
icle
s (M
eV-1 m
sr-1) 107
106
105
circularpolarization
0 10 20 30 5040 60 70 80 90energy (MeV)
1
10
100
part
icle
s (a
. u.)
t = 45 fst = 221 fs
linearpolarization
0 10 20 30 5040 60 70 80 90energy (MeV)
1
10
100
part
icle
s (a
. u.)
carbon C6+t = 45 fst = 221 fscarbon C6+
experiment
simulationsimulation
experiment
0
0.02
0.04
0.06
0.08
circularpolarization
3.0 3.1 3.2 3.3 3.4 3.5x (λ)
p x (m
i c )
carbon C6+
t = 45 fs
0
0.02
0.04
0.06
0.08
3.0 3.2 3.4 3.6 3.8 4.0x (λ)
p x (m
i c )
linearpolarization
carbon C6+
t = 45 fs
measured proton and C6+ spectra
2D PIC results for C6+
C6+ spectrum at different times
C6+ phase space
2 3 4 5 6 7x (λ)
linearpolarization
electrondensity
circularpolarization
electrondensity
8
-4
-2
0
2
4
y (λ
)
2 3 4 5 6 7x (λ)
8
-4
-2
0
2
4
y (λ
)
0
5
10
15
20
25
0
5
10
15
20
25
linearpolarization
carbondensity
2 3 4 5 6 7x (λ)
8
-4
-2
0
2
4
y (λ
)
circularpolarization
carbondensity
2 3 4 5 6 7x (λ)
8
-4
-2
0
2
4
y (λ
)
0
1
2
3
4
0
1
2
3
4
linear polarization circular polarization
strong expansion driven by hot electrons
ballistic acceleration of whole focal volume
Gaussian focal spot causes foil to bend
Strong electron heating sets in due to oblique incidence on walls
Rapid foil expansion / termination of RPA
Potential solutions: increased focal spot size
higher laser intensities
pre-curved targets
circularpolarization
electrondensity
2 3 4 5 6 7x (λ)
8
-4
-2
0
2
4
y (λ
)
0
5
10
15
20
25
collimated ion beam from back surface (TNSA)
divergent ion beam from front surface
TNSA ion now accelerated into 4
highly directed shock accelerated ion beam
vs /c = aL / 2 (me /mi)1/ 2(nc /ni)
1/ 2shock speed:
First experimental demonstration of radiation pressure acceleration (RPA) to become the dominant ion acceleration mechanism when using nm-thin foil targets and circular polarization
Highly promising route towards intrinsically mono-energetic, dense ion beams at large conversion efficiencies
For the moment, keeping the monochromaticity by suppressing electron heating over longer times remains a demanding challenge
MAP biomedical beam line is currently being set up at MPQ
magnetic chicane will be used as interim energy filter